OPEN SOURCE DIY Mic Project - ORS 87 - Stripped Down u87

[micolas]

Ok, this will be the one! Thank you very much @micolas!
So, as a summary:

• Remove HI-Z traces
• Add ground plane connecting to body using the screws
• Remove redundant/multiple options
• Use WIMA MKS-4 1uf cap

Ugly coupling pads will remain . They do make a difference.

I would also think about the possibility of using several pinout types for jFET, in order not to contort the terminals.
The circuit works with BF, 2N,2SK,J etc.

 

[homero.leal]

I would also think about the possibility of using several pinout types for jFET, in order not to contort the terminals.
The circuit works with BF, 2N,2SK,J etc.

But we want simplify things, don't we? This will cause confusion, as with the traces.

 

[micolas]

But we want simplify things, don't we? This will cause confusion, as with the traces.

There would be a version X with just one extra hole on request for advanced people who want to test different jFETs.
In the D G S D configuration, all pinout types can be connected.

 

[micolas]

There would be a version X with just one extra hole on request for advanced people who want to test different jFETs.
In the D G S D configuration, all pinout types can be connected.

@homero.leal
Or, even simpler: a single PCB for all, but with an extra hole for one more D connection, symmetrical to S, but without writing on the board. Beginners are guided by the writing and ignore the additional hole.

 

[homero.leal]

@homero.leal
Or, even simpler: a single PCB for all, but with an extra hole for one more D connection, symmetrical to S, but without writing on the board. Beginners are guided by the writing and ignore the additional hole.

Genious!!!!! Great idea. Will try to do it with the V1.2 board.

 

[micolas]

Genious!!!!! Great idea. Will try to do it with the V1.2 board.

@Khron 's fault for getting me interested in the J113 which has a different pinout than the 2N3819. That's how I got the idea.

 

[eso]

And... now that you mention about version 1.2, what additional changes would you like to have?
I expect to update it next weekend.
Regards!

I would really like to see an updated BOM for whatever form V1.2 takes.

After ordering parts based on V1 and having the parts labeled per the numbering on V1 I received V1.1 boards (I had not gone far enough through the thread to see where it update happened an the original link defaulting to V1.1). Then with the understanding that the V1.1 numbering is to correspond to the original oneroomstudio BOM I realized that several parts values are very different. It creates a lot of confusion for a neophyte like me–I can follow the BOM, stuff and solder the parts in the board but I'm really clueless to the intricacies of electronics.

Anyway, big thanks to Homero, Oneroomstudio, Wordsushi and everyone else contributing to this effort.

I just assembled my first effort but have not tested it yet.

A $20 Chinese mic cannibalized for the chassis and case, a bunch of parts and a 3D printed cartridge stand and I think I've got a decent mic here. This one has the T-13 x-former for the moment until I get the Cinemag 13113 transformers

 

[Khron]

My attempt to PCB Star Grounding

PS: I really regret i didn't notice this yesterday, but...

How exactly is a SERIES string of "ground" connections (as illustrated in the PCBway schematic) supposed to be STAR grounding? Seems to me that's pretty much the exact opposite...

 

[ofi]

And... now that you mention about version 1.2, what additional changes would you like to have?
I expect to update it next weekend.
Regards!

I would like to see some grounded screw holes on the top and maybe on the bottom of the pcb thanks.

 

[Khron]

I would like to see some grounded screw holes on the top and maybe on the bottom of the pcb thanks.

Those are only relevant if the screw holes happen to match the mic chassis you're using. All the copper plating in the world won't help if the PCB's fastened to the chassis with zap-straps / cable ties...

 

[micolas]

Those are only relevant if the screw holes happen to match the mic chassis you're using. All the copper plating in the world won't help if the PCB's fastened to the chassis with zap-straps / cable ties...

Exact!
I mentioned the screw holes (for mechanical fastening and connection to GND) yesterday in the suggestions for the new version of @homero's PCB

 

[micolas]

@anvl

Turret (PTFE insulated pin) can be found at Mouser in various shapes and sizes
This is suitable for ors87
https://ro.mouser.com/ProductDetail/Keystone-Electronics/11218?qs=do/%2B0R7m72fuB8hSRPx0tw==

 

[homero.leal]

I would really like to see an updated BOM for whatever form V1.2 takes.

After ordering parts based on V1 and having the parts labeled per the numbering on V1 I received V1.1 boards (I had not gone far enough through the thread to see where it update happened an the original link defaulting to V1.1). Then with the understanding that the V1.1 numbering is to correspond to the original oneroomstudio BOM I realized that several parts values are very different. It creates a lot of confusion for a neophyte like me–I can follow the BOM, stuff and solder the parts in the board but I'm really clueless to the intricacies of electronics.

Anyway, big thanks to Homero, Oneroomstudio, Wordsushi and everyone else contributing to this effort.

I just assembled my first effort but have not tested it yet.

A $20 Chinese mic cannibalized for the chassis and case, a bunch of parts and a 3D printed cartridge stand and I think I've got a decent mic here. This one has the T-13 x-former for the moment until I get the Cinemag 13113 transformers

My mistake @eso, apologies for that. I should have created a new project page for V1.1 instead of modifying the original project.
I promise I will create a new project page for V1.2. And don't worry, V1.1 just adds additional caps, but V1 parts are the same. If it helps, I can send you original V1 schematic on a DM.
Regards!

HL

 

[homero.leal]

PS: I really regret i didn't notice this yesterday, but...

How exactly is a SERIES string of "ground" connections (as illustrated in the PCBway schematic) supposed to be STAR grounding? Seems to me that's pretty much the exact opposite...

Could you note ground trace for filtering caps is separate from ground trace for signal, and that they join only very near to the ground pad of the PCB? This idea is from beloved guru and friend, @ricardo Lee as a recommendation for Low Noise designs.

 

[Khron]

Like i said, IF there were any meaningful currents involved, i could perhaps see the point, but since the U87's supposed to draw a measly 0.4mA in total.....

But that series string of ground connections still means the bottom of the gate resistor, AND the feedback-filter network, WILL be modulated up and down by the voltage drop across that looooong thin ground trace, from the current going through the JFET, will it not? Sure, that might not show up as noise, but as some form of distortion, but... what do i know?

Call me weird, but i'll stick with my big fat low-impedance ground plane...

 

[eso]

My mistake @eso, apologies for that. I should have created a new project page for V1.1 instead of modifying the original project.
I promise I will create a new project page for V1.2. And don't worry, V1.1 just adds additional caps, but V1 parts are the same. If it helps, I can send you original V1 schematic on a DM.
Regards!

HL

I think I've got it all sorted out. I have copies of the V1 board layout, the schematic you posted back then and the BOM for V1. It was when I was revising the part #s from V1 to V1.1 that I noticed several different part values between your schematic and Oneroomstudio's original BOM. That is where I am the most confused here.

On a side note, I got the TSC-2 cartridges when I really only needed the TSC-1... How much additional work is needed to add pattern switching to these mics?

 

[Khron]

How much additional work is needed to add pattern switching to these mics?

You'd need to add some form of DC-DC converter, to get a +/-60v for the simplest way to switch patterns. On that note, if you're not in the greatest of hurries...

https://groupdiy.com/threads/feeler...-upgrade-boards-opamp-jfet-u87a-fet847.87606/

 

[homero.leal]

Like i said, IF there were any meaningful currents involved, i could perhaps see the point, but since the U87's supposed to draw a measly 0.4mA in total.....

Or... if you have a HI-Z area that could be disturbed by parasitic currents.

 

[micolas]

On a side note, I got the TSC-2 cartridges when I really only needed the TSC-1.

No, you don't need TSC-1.
It is very good that you got the TSC-2 double sided capsule from JLI. It is produced by TAKSTAR (is the one used in AKG P420), and the TSC-1 single side is produced by AYM, it is not the one used in AKG Perception, P220.
There is no connection between them, they sound different.
Even between the 420 and 220 capsules there are sound differences.
In fact the TSC-2 will sound better in cardioid than a single side capsule, will have better rear rejection .
TSC-2 is more suitable for the sound of the U87.
Maybe some have a different opinion but my belief is that you will not get the behavior of the U87 (which has a double sided capsule and two central screws), with a single sided capsule whose free rear membrane, fixed only on the circumference, vibrates/resonates/damps differently.

 

[eso]

In fact the TSC-2 will sound better in cardioid than a single side capsule, will have better rear rejection and has a frequency response more suitable for the sound of the U87.

OK, how do I wire the cartridge to accomplish this? Do i only connect the front side of the diaphragm and a ground? or is the rear lead grounded?

I haven't landed the contacts for the cartridge yes because I wasn't sure. I've got a ground lead connected using one of the mounting screws for the cartridge (seemed like a good path not requiring removing one of the cartridge assembly screws) but not fully sure how to proceed.

Thanks

eso